Concrete in Australia Vol 38 No 1 43
was retained, thus indicating the integrity of the polyethylene
curing.
Tables 1, 2 and 3 show the test results for compressive
strength, drying shrinkage and volume of permeable void
(VPV/permeability) respectively.
Table 1 shows that on the average, with the exception of the
initial test panel, the minimum required 28 day compressive
strength of 55 MPa was on the borderline of acceptability.
Although it is considered that with more experience, further
refinement of the mix design and manipulation of the alkaline
activator dosage rates the strengths should be readily achieved
on a consistent basis. e results in Table 3 indicate that the
maximum limitations of drying shrinkage of 750 microstrain
can be achieved.
Table 3 however, indicates that the geopolymer concrete used
in the precast footway panels was not able to achieve the VPV
requirements of Section 610 for an equivalent 55 MPa concrete.
e table indicates that the VPV results ranged between 19.5%
and 21.7% for both cylinders and concrete cores far exceeding
the maximum allowable limits of 12% for rodded cylinders
and 14% for concrete cores for an equivalent concrete grade of
VR470/55 as specified in Section 610.
4.1.1 Geopolymer precast footway panels --
Observations
e general observations relating to the geopolymer footway
panels trial can be summarised as follows:
• As indicated in Table 1, strength development was initially
an issue and as such acceleration of strength development
was required due to the geopolymer mix design used and
the urgency with which the mix design was developed at the
time.
• e casting bed was heated to a temperature range of
between 18 °C and 35 °C with an even heat distribution
following some initial problems. It was considered that
the requirement for bed heating may be eliminated with
improvements in raw materials and the geopolymer mix
design.
• e overall slump retention, discharge, kibble transfer
and placement and consolidation under vibration were
considered satisfactory.
• Finishing was found to be somewhat difficult with coarse
aggregate difficult to get down from the surface and paste
was brought to the surface using an expanded mesh roller
which was also forcing down the coarse aggregate. e mix
was found to be stickier than conventional concrete and
as such water spray was applied on the surface to facilitate
finishing due to stiffness of the mix. Generally longer setting
times were indicative of higher water content. Optimal
finishing includes screeding then waiting as long as possible
before final finish. Stipple finish was found to work better
than broomed and was selected for finish of the panels.
• With respect to curing, the precast practice to cover in
polyethylene plastic was found to be sufficient.
• e units stripped well and lifting was achieved within
normal times of 16-20 hours, with lifting strengths in the
order of 15 MPa to 20 MPa.
4.2 Insitu geopolymer concrete landscape
retaining walls
Construction of the insitu geopolymer concrete landscape
retaining walls was undertaken utilising conventional
techniques for formwork construction, concrete placement
by pumping, compaction with a poker vibrator, finishing and
curing with polyethylene plastic (Figure 4).
e quality of the landscape retaining walls ranged from
Figure 4. Construction of geopolymer concrete retaining walls using conventional techniques.
Figure 5. Surface finish of geopolymer concrete retaining walls.